Since glass or plastics which are used as transparent substrates of varied types of including face-plates for Cathode ray tube (CRT), liquid crystal display (LCD), etc. are insulating materials, the surface thereof is subject to static electrification and hence the substrate surface tends to attract dusts or the like. Furthermore, in electrodisplay devices such as LCD, etc., poor performance is sometimes caused by the presence of static electricity. For solving such problems as referred to above, attempts have often been made to prevent such substrates as glass, plastics, etc. from being electrostatically charged by virtue of imparting electrical conductivity to the surface thereof.
In order to impart electrical conductivity to substrates, metallic thin films or conductive inorganic oxide coatings are deposited on the surface of substrate by the vapor phase method such as the CVD method, the PVD method and vapor deposition method, etc. In an attempt to impart electrical conductivity to the substrate surface by the vapor phase method, however, there are such problems in that vacuum deposition apparatuses are required therefor, and the surface area or shape of the substrate, on which the desired coating is formed, is restricted by the size of said apparatuses to be employed.
In light of the above problems, a process for imparting electrical conductivity to substrates has been proposed, which process comprises coating the substrate on the surface thereof with conductive coating materials obtained by dispersing conductive substrates in binder resins.
However, when attempt were made to form conductive coatings on substrates by using conductive coating materials obtained by dispersing conductive substances in binder resins, such as acrylic resins, butyral resins, vinyl chloride/vinyl acetate copolymer resins, etc., there occurred were such serious problems that the conductive coatings formed thereby were found poor in transparency, scratch resistance, solvent resistance or in adhesion to the substrates, though said conductive coatings were excellent in electrical conductivity.
Under such circumstances, there has earnestly been desired of coating liquids for forming conductive coatings which are excellent in scratch resistance, solvent resistance and in adhesion to substrates as well as transparency.
Apart from the purpose of forming conductive coatings on substrates, however, Japanese Patent L-O-P Publn. No. 100943/1982 discloses silicon oxide coatings containing 1-30 mol % of zirconium oxide with the view of protecting the substrate surface and inhibiting reflection therefrom. In this publication, it is stated that in the zirconium oxide-silicon oxide coatings there are used, as the zirconium compounds, zirconium chloride such as ZrCl.sub.2, ZrCl.sub.3 or ZrCl.sub.4 ; zirconium nitrate such as Zr(NO.sub.3).sub.4 O5H.sub.2 O; zirconium alkoxides and zirconium diketonates.
However, when an attempt is made to form the zirconium oxide-silicon oxide coatings by using coating liquids containing zirconium chloride, zirconium nitrate, zirconium alkoxide or zirconium diketonate and silicon alkoxide, it has been found by the present inventors that there is such a serious problems that because of instability in water of zirconium chloride and zirconium nitrate, the coating liquids containing the same cannot be preserved over a long period of time and have a short pot-life. Moreover, even if zirconium oxide-silicon oxide coatings were formed by the use of the above-mentioned coating liquids containing zirconium chloride and the like, it was still necessary to heat the resultant coatings at a temperature of at least 450.degree. C. Moreover, the coating liquids as described above involved such a problem that said coating liquids must be adjusted to a pH of 2-6 by the fresh addition thereto of a mineral acid such as hydrochloric acid at the time when silicon alkoxides contained therein are hydrolyzed.
On one hand, face-plates of display devices are required in some cases to have a specular reflection reducing effect (hereinafter called non-glare) in order to inhibit glaring of said face-plates, in addition to their antistatic effect. In order to impart non-glare and antistatic effect to face-plates of display devices, a process designed for the purpose intended is disclosed, for example, in Japanese Patent L-O-P Publn. No. 16452/1986, wherein the face-plate composed of glass or plastics is previously heated, and a colloidal solution of silicon compound such as partially hydrolyzed silicic acid ester, a solution of reactive silicon compound such as silicon tetrachloride, or a solution prepared by mixing the above-mentioned solution with a water-soluble compound of inorganic metal such as platinum, gold, palladium, tin or the like is sprayed over said face-plate to form thereon a finely irregular coating, followed by drying and heating.
Further, a process for forming a coating layer on a face-plate of Braun tube is also disclosed, for example, in Japanese Utility Model L-O-P Publn. No. 168951/1984, wherein tin oxide or indium oxide and silicon oxide are mixed or laminated by the vacuum deposition or dip method to form the coating layer on the face-plate.
In face-plate of display devices processed by the above-mentioned processes, however, the non-glare effects attained were found insufficient, and the antistatic effects varied, depending on the ambient temperature and humidity, and under certain circumstances the resolving power of the display devices were decreased by the presence of the coating formed on the face-plate. Further, the finely irregular coatings, as formed, were weak in adhesion to the face-plate and easily peeled off therefrom, and were easily scratched being low in mechanical strength. Moreover, the coat tended to peel off or elute due to a deficiency in permanence properties such as acid resistance, alkali resistance, resistance to saline solutions and to water; thus, adequate non-glare and antistatic effects could not be maintained over a long period of time.
The present invention is intended to solve such problems associated with the prior art as mentioned above, and an object of the invention is to provide coating liquids for forming conductive coatings, said coating liquids being capable of forming on substrates such as glass, plastics, etc. the conductive coatings excellent in scratch resistance, permanence properties and adhesion to the substrates as well as in transparency and, at the same time, which are capable of being preserved with excellent stability over a long period of time.
A further object of the present invention is to provide glass or plastic substrates provided with transparent conductive coatings formed by the use of such coating liquids as mentioned above, said conductive coatings being excellent in transparency, scratch resistance, permanence properties, adhesion to the substrates and antistatic effect, or glass or plastic substrates provided likewise with transparent conductive coatings having non-glare in addition to the above-mentioned functions. Another object of the present invention is to provide display devices having face plate provided with transparent conductive coatings having the above-mentioned functions.